JP2013205585A - Image forming apparatus and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus or the like, which generates less positional shift in each color image.SOLUTION: An image forming apparatus comprises: image forming units for forming images using a plurality of colors; an image output circuit 64 and an image quality adjustment pattern data storage part 65 for allowing each of the image forming units to form two or more successive position control marks in a same color for one pattern used for correcting a positional shift of a formed image; an intermediate transfer belt having the formed position control marks sequentially transferred thereon; a detection sensor part 80 including a light source for outputting light toward the intermediate transfer belt and the position control marks, and a light reception part for receiving reflection light reflected thereon and making it detection signals for detecting the position control marks; and a CPU 61 for specifying by the detection signals a position between the two successive position control marks, and executes a positional shift correction of an image formed by the image forming unit.

Description

  The present invention relates to an image forming apparatus and a program.

In Patent Document 1, a pair of single-color patterns obtained by transferring only a yellow developer is formed on both sides along the moving direction of the transport belt with a black single-color pattern sandwiched between yellow registration marks. However, the same registration mark is disclosed for magenta and cyan registration marks.
Japanese Patent Application Laid-Open No. H11-228707 describes a position detection color image pattern when a position ratio of a peak value of the sensor output of an optical sensor is set as a threshold value and the sensor output reaches the threshold value. A multicolor image forming apparatus that detects the trailing edge is disclosed.

JP 2009-244505 A JP 2010-160317 A

  Here, in an image forming apparatus that forms an image using a plurality of colors, it is desirable that the positional deviation of each color image is smaller.

  According to the first aspect of the present invention, there is provided an image forming unit that forms an image using a plurality of predetermined colors, and an image correction unit that is used for correcting misalignment of an image formed by the image forming unit. An index forming means for forming two or more indices in the same color continuously by the image forming section for one mold, and an image holding body to which the image correction index formed by the image forming section is sequentially transferred A light source that emits light toward the image correction index, and a light reception signal that receives reflected light reflected from the image holding body and the image correction index and detects the image correction index A position specifying means for specifying a position between two consecutive image correction indices from a detection signal obtained from the light receiving section of the detection means, and the position specifying means. Identified 2 above From a position between the image correcting indication of an image forming apparatus characterized by comprising: a positional deviation correcting part for performing positional deviation correction for the image to be formed by the image forming unit.

According to a second aspect of the present invention, in the image according to the first aspect, the index forming unit forms a color other than black as the two consecutive image correction indexes. Forming device.
A third aspect of the present invention is the image forming apparatus according to the first or second aspect, wherein the detection unit does not have an optical element that refracts the light on the optical path of the light.
The invention according to claim 4 is characterized in that the position specifying means specifies a position between two consecutive image correction indices by detecting a maximum value of the detection signal. 4. The image forming apparatus according to any one of items 1 to 3.

  According to the fifth aspect of the present invention, an image correction index used for correcting misalignment of an image formed in an image forming unit that forms an image using a plurality of predetermined colors on a computer. A function of forming two or more consecutive images of the same color in the same color by the image forming unit, a light source that emits light toward the image correction index, an image holding body, and the image correction index reflected from the image A light receiving unit that receives reflected light and detects it as a detection signal for detecting the image correction index, and a function for obtaining the detection signal from the detection unit, and a detection obtained from the light receiving unit of the detection unit The function of specifying the position between two consecutive image correction indices from the signal and the position between the two specified image correction indices of the image formed by the image forming unit A machine that corrects misalignment If a program for realizing the.

According to the first aspect of the present invention, it is possible to provide an image forming apparatus in which each color image is less misaligned than when the present invention is not adopted.
According to the second aspect of the present invention, two or more image correction indices can be formed continuously for one mold for a color that produces diffusely reflected light.
According to the third aspect of the present invention, the detection means can be configured at a lower cost than when the present invention is not adopted.
According to the invention of claim 4, it is possible to specify the center position of two consecutive image correction indices for one mold.
According to the fifth aspect of the present invention, compared with the case where the present invention is not adopted, the computer can realize a function of reducing the positional deviation of each color image in the image forming unit.

1 is a diagram illustrating a configuration of an image forming apparatus to which the exemplary embodiment is applied. It is a figure explaining the structure for performing position shift control. It is a figure explaining the structure of the reading function part which reads the pattern for image quality adjustment in a detection sensor part. It is a block diagram explaining the function of a main control part and a detection sensor part. It is a figure explaining the structure of the detection circuit with which the detection sensor part was equipped. It is a flowchart which shows the process sequence at the time of the main control part performing position shift control with respect to the image formed in each image forming unit. (A) is a figure which shows an example of the image quality adjustment pattern of this Embodiment. FIG. 6B is a diagram illustrating an example of a conventional image quality adjustment pattern. It is a timing chart explaining the signal which a detection sensor part generates by reading a position control mark. (A)-(c) is the figure explaining the pattern detection signal of this Embodiment. (A)-(c) is a figure explaining the pattern detection signal when the conventional pattern for image quality adjustment is used. It is a figure explaining the calculation method of the amount of position shifts using the mark for position control. FIG. 6 is a diagram showing spectral reflectances with respect to light wavelengths for toners of Y, M, C, and K colors. It is a figure which shows an example of the pattern for image quality adjustment at the time of using the thing of luminescence center wavelength 680nm as LED.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
<Description of Image Forming Apparatus>
FIG. 1 is a diagram illustrating a configuration of an image forming apparatus 1 to which the exemplary embodiment is applied. An image forming apparatus 1 shown in FIG. 1 is a so-called tandem type digital color printer, and an image forming process unit 20 that forms a color image based on image data, and a main control that controls the operation of the image forming process unit 20. Part 60.

The image forming process unit 20 forms each color toner image of yellow (Y), magenta (M), cyan (C), and black (K), which are arranged in parallel at a predetermined interval. As an example, four image forming units 30Y, 30M, 30C, and 30K (hereinafter also collectively referred to as “image forming unit 30”) are provided. In addition to this, for example, in addition to those that form toner images of each color such as light cyan (LC), light magenta (LM), and corporate color, an image forming unit of five or more colors may be provided.
The image forming unit 30 is formed on the photosensitive drum 31, a photosensitive drum 31 on which an electrostatic latent image is formed while rotating in the direction of arrow A, a charging roll 32 that charges the surface of the photosensitive drum 31, and the photosensitive drum 31. A developing device 33 for developing the electrostatic latent image and a drum cleaner 34 for cleaning the surface of the photosensitive drum 31 after the primary transfer are provided. The developing device 33 disposed in each image forming unit 30 generates an electrostatic latent image on the photosensitive drum 31 with each color toner of Y, M, C, and K supplied from the toner containers 35Y, 35M, 35C, and 35K. develop.

  The image forming process unit 20 also includes a laser exposure device 26 as an example of an exposure unit that exposes each photosensitive drum 31 provided in each image forming unit 30 with, for example, laser light, and each photosensitive member of each image forming unit 30. Each color toner image formed on the body drum 31 is multiplex-transferred, and an intermediate transfer belt 41 as an example of a transfer member that conveys the multi-transferred color toner images while holding them. Further, a primary transfer roll 42 that sequentially transfers (primary transfer) each color toner image of each image forming unit 30 to the intermediate transfer belt 41 in the primary transfer portion Tr1, and a superimposed toner image transferred onto the intermediate transfer belt 41. A secondary transfer roll 40 that performs batch transfer (secondary transfer) onto a sheet P (P1, P2), which is a recording material (recording sheet), in the secondary transfer unit Tr2, and fixes the second transferred image on the sheet P And a fixing device 25 to be operated.

  In addition, detection as an example of a detection unit is located upstream in the moving direction of the intermediate transfer belt 41 from the secondary transfer portion Tr2 (secondary transfer roll 40) and downstream of the black image forming unit 30K. A sensor unit 80 is disposed. The detection sensor unit 80 is disposed on the end side in a direction orthogonal to the moving direction of the intermediate transfer belt 41 (see FIG. 2 in the subsequent stage). Then, an image quality adjustment pattern (image quality adjustment toner image) for alignment that is formed in the region on the end side of the intermediate transfer belt 41 is read, and the positional deviation control of each color image quality adjustment toner image described later is performed. The position of each image quality adjustment toner image for performing the above is detected. That is, the intermediate transfer belt 41 functions as an image holding body to which each image quality adjustment toner image formed by the image forming unit 30 is sequentially transferred.

The laser exposure device 26 includes a semiconductor laser 27 as a light source, a scanning optical system (not shown) that scans and exposes a laser beam to the photosensitive drum 31, and a rotary polygon mirror (polygon mirror) 28 formed of, for example, a regular hexagonal body. And a laser driver 29 for controlling the driving of the semiconductor laser 27. The laser driver 29 acquires image data that has undergone image processing, a control signal for correcting exposure timing in the main scanning direction and the sub-scanning direction, a control signal for correcting the laser light amount, and the like from the main control unit 60. The lighting control of the semiconductor laser 27 is performed.
The primary transfer roll 42 is supplied with a primary transfer bias voltage from a primary transfer power source (not shown), and primarily transfers each color toner image onto the intermediate transfer belt 41. The secondary transfer roll 40 is supplied with a secondary transfer bias voltage from a secondary transfer power source (not shown), and secondarily transfers the color toner images onto the paper P.
The fixing device 25 fixes the toner image on the paper P by passing the paper P holding the unfixed toner image between a fixing roll having a heating source therein and a pressure roll.

  In the image forming apparatus 1 according to the present embodiment, the laser exposure device 26 is used as an example of the exposure unit. However, an organic EL (Electro-Luminescence) using an LED (Light Emitting Diode) array as an example of the exposure unit. ) May be used.

<Description of image forming operation>
The image forming apparatus 1 acquires image data from a personal computer (PC) or an image reading device (scanner) (not shown), performs predetermined image processing on the acquired image data, and decomposes the image data for each color. Image data (each color image data) is generated. Then, the generated color image data is supplied to the laser exposure device 26 of the image forming process unit 20.
Meanwhile, the photosensitive drum 31 is charged by the charging roll 32. The laser exposure device 26 scans and exposes the photosensitive drum 31 charged by each image forming unit 30 with laser light whose lighting is controlled based on the supplied color image data and various control signals. Thereby, an electrostatic latent image of each color is formed on each photosensitive drum 31. The formed electrostatic latent image is developed by each developing device 33, and each color toner image is formed on each photosensitive drum 31.

Each color toner image formed by each image forming unit 30 is primary-transferred sequentially by a primary transfer roll 42 onto an intermediate transfer belt 41 that circulates in the direction of arrow B in FIG. As a result, a superimposed toner image is formed on the intermediate transfer belt 41 by superimposing the toner images of the respective colors. The superimposed toner image is conveyed toward the secondary transfer portion Tr2 in which the secondary transfer roll 40 and the backup roll 49 are arranged as the intermediate transfer belt 41 moves.
On the other hand, the image forming apparatus 1 is provided with a plurality of sheet holding units 71A and 71B, for example. Then, for example, based on an instruction input by a user from an operation input panel (not shown), for example, the paper P1 held in the paper holding unit 71A is taken out. The taken paper P1 is conveyed one by one along the conveyance path R1, and is conveyed to the secondary transfer unit Tr2 in accordance with the timing at which the superimposed toner image is conveyed to the secondary transfer unit Tr2 on the intermediate transfer belt 41. The The superimposed toner images are secondarily transferred collectively onto the paper P1 by the action of the transfer electric field formed on the secondary transfer portion Tr2.
Note that the conveyance of the paper P to the secondary transfer unit Tr2 is used during duplex printing on the paper P in addition to the conveyance path R1 through which the paper P1 and P2 held by the paper holding units 71A and 71B are conveyed. This is also performed from the double-sided conveyance path R2 and the conveyance path R3 from the manual sheet holding unit 75 used when manually feeding the sheet P.

Thereafter, the sheet P1 on which each color toner image is electrostatically transferred in the secondary transfer portion Tr2 is peeled off from the intermediate transfer belt 41 and conveyed toward the fixing device 25. In the fixing device 25, each color toner image is fixed on the paper P1. Then, the paper P1 on which the fixed image is formed is carried out to a paper stacking unit 79 provided in the discharge unit of the image forming apparatus 1. On the other hand, the toner (transfer residual toner) adhering to the intermediate transfer belt 41 after the secondary transfer is removed by a belt cleaner 45 disposed in contact with the intermediate transfer belt 41 to prepare for the next image forming cycle.
In this manner, image formation in the image forming apparatus 1 is repeatedly executed for the designated number of sheets.

<Description of misregistration control>
Next, image position correction control (so-called “registration control”: hereinafter “position shift control”) for correcting the position shift of each color toner image formed by each image forming unit 30 will be described.
The photosensitive drum 31 disposed in each image forming unit 30 varies in relative position with respect to the intermediate transfer belt 41 due to, for example, fluctuations in environmental temperature or temperature rise in the apparatus. Further, the developer in the photosensitive drum 31 and the developing device 33 arranged in each image forming unit 30 is, for example, an internal factor such as an accumulated operation time or a rest time of the image forming apparatus 1 or a usage history, and further, The state changes due to external factors such as temperature and humidity environment.
Therefore, in the image forming apparatus 1 of the present embodiment, for example, when the in-machine temperature fluctuates beyond a predetermined temperature, or when the image forming operation exceeds a predetermined number of cycles, For example, when the main power source (not shown) of the image forming apparatus 1 is turned on or when the front cover (front door) of the image forming apparatus 1 is opened, the previous image forming operation in the image forming apparatus 1 is performed. In a situation where a long time has passed and the temperature environment in the image forming apparatus 1 is assumed to fluctuate, the positional deviation of each color toner image on the intermediate transfer belt 41 is adjusted within an allowable level. In addition, misregistration control (image position adjustment control, registration control) is performed to suppress image color misregistration.

<Description of Configuration for Executing Misregistration Control>
Next, FIG. 2 is a diagram illustrating a configuration for executing the positional deviation control. As shown in FIG. 2, in the image forming apparatus 1 of the present embodiment, black (K) is on the upstream side in the moving direction of the intermediate transfer belt 41 as viewed from the secondary transfer portion Tr <b> 2 (secondary transfer roll 40). The detection sensor unit 80 is disposed downstream of the photosensitive drum 31 disposed in the image forming unit 30K. The detection sensor unit 80 is disposed on the end side in the direction orthogonal to the moving direction of the intermediate transfer belt 41. In the present embodiment, the detection sensor unit 80 is disposed in an end region on the intermediate transfer belt 41 opposite to a region where scanning exposure is started on the photosensitive drum 31 by the laser exposure device 26. The detection sensor unit 80 may be arranged near the center in the direction orthogonal to the moving direction of the intermediate transfer belt 41, and the position in the main scanning direction is not particularly limited.

The main control unit 60 has an image quality adjustment pattern T (image quality adjustment pattern) in a region on one end side where the detection sensor unit 80 on the intermediate transfer belt 41 faces the image forming units 30Y, 30M, 30C, and 30K. Instruct to form a toner image. Accordingly, when the image quality adjustment pattern T is formed on the intermediate transfer belt 41, the detection sensor unit 80 reads it and sends a detection signal related to each image quality adjustment pattern T to the main control unit 60.
The main control unit 60 generates a control signal for correcting the exposure timing in the main scanning direction and the sub-scanning direction for each image forming unit 30 based on the detection signal from the detection sensor unit 80. Then, these control signals are transmitted to the laser driver 29 of the laser exposure device 26.

<Description of configuration of detection sensor unit>
Next, the configuration of the reading function unit that reads the image quality adjustment pattern T in the detection sensor unit 80 will be described.
FIG. 3 is a diagram illustrating the configuration of the reading function unit that reads the image quality adjustment pattern T in the detection sensor unit 80. As shown in FIG. 3, the detection sensor unit 80 irradiates the toner image holding surface of the intermediate transfer belt 41 and emits light toward the image quality adjustment pattern T as an example of a light source that emits light (LED having an emission center wavelength of 940 nm). Light Emitting Diode) 81, the intermediate transfer belt 41 irradiated by the LED 81, and reflected light from the image quality adjustment pattern T formed on the intermediate transfer belt 41 are received, and a current value having an intensity corresponding to the amount of received light is obtained. An output PD (Photo Diode) 83 is provided as an example. That is, the PD 83 functions as a light receiving unit that receives the reflected light reflected from the image quality adjustment pattern T and uses it as a detection signal for detecting the image quality adjustment pattern T.

  These LEDs 81 and PD 83 are accommodated in a case 84 as an example of a support member having a downward opening so as to be arranged in a direction perpendicular to the moving direction of the intermediate transfer belt 41. The light emitted from the LED 81 passes through an exit slit 84a provided in the case 84, and illuminates the surface of the intermediate transfer belt 41 at an angle of 80 °, for example. In addition, the case 84 is provided with an incident slit 84 c for allowing the reflected light from the image quality adjustment pattern T formed on the surface of the intermediate transfer belt 41 and the intermediate transfer belt 41 to pass toward the PD 83. The incident slit 84 c is provided in a direction of, for example, 100 ° with respect to the surface of the intermediate transfer belt 41.

  In other words, the exit slit 84a and the entrance slit 84c are the same in the direction perpendicular to the moving direction of the intermediate transfer belt 41 (the direction of both ends of the intermediate transfer belt 41) with the normal line N related to the surface of the intermediate transfer belt 41 as the center. It is formed to be inclined by an inclination angle (here, 10 °). As a result, the reflected light reflected by the intermediate transfer belt 41 and the image quality adjustment pattern T is incident on the PD 83 from the irradiation light toward the intermediate transfer belt 41 by the LED 81.

  The exit slit 84a and the entrance slit 84c are formed so that the diameters thereof become smaller as the distance from the LED 81 or the PD 83 increases. In the opening (aperture) where light is emitted from the exit slit 84a and the opening where reflected light is incident on the entrance slit 84c, the aperture shape is the smallest. Thereby, the opening part of the exit slit 84a and the opening part of the entrance slit 84c of the present embodiment function as a diaphragm part arranged at a position on the optical path of light.

The function of the opening portion of the entrance slit 84c as the aperture portion is to suppress the incidence of diffused light among the light reflected by the image quality adjustment pattern T. That is, the PD 83 is arranged at a position where the regular reflection light is incident in the above-described configuration, but is also at a position where the diffused light can be incident. Therefore, if diffused light is incident, the pattern detection signal generated by the PD 83 may be disturbed, and the image quality adjustment pattern T may not be read normally. For this reason, the entrance slit 84c has a stop shape that decreases in diameter as it moves away from the PD 83, thereby suppressing the incidence of diffused light so that the pattern detection signal is not easily disturbed by the diffused light.
In order to suppress the incidence of diffused light, the diameter of the entrance slit 84c, that is, the location where the light reflected by the image quality adjustment pattern T enters the entrance slit 84c is preferably 1.5 mm or less. In the present embodiment, the diameters of the openings of the exit slit 84a and the entrance slit 84c are both about 1.1 mm. However, in this embodiment, since part of the diffused light is also incident in this form, the influence of the diffused light is suppressed by a method described in detail later.

  Note that, from the viewpoint of suppressing the incidence of diffused light, a function as a diaphragm by the opening of the entrance slit 84c is necessary, but a function as a diaphragm by the opening of the exit slit 84a is not necessarily required. However, the light spot of the light irradiated to the image quality adjustment pattern T can be made smaller by causing the opening of the exit slit 84a to also have a function as a diaphragm. Therefore, there are advantages that the reading accuracy of the image quality adjustment pattern T is further improved and that diffused light is less likely to be generated.

  Even if no diaphragm is provided as in the present embodiment, a lens or the like is provided in the entrance slit 84c or in both the exit slit 84a and the entrance slit 84c, thereby suppressing the incidence of diffused light. It is possible to do. However, in that case, since it is necessary to provide a lens etc. separately, the manufacturing cost of the detection sensor part 80 becomes higher. The detection sensor unit 80 of the present embodiment is superior in that the manufacturing cost is lower. The detection sensor unit 80 of this embodiment is characterized in that it does not have an optical element that refracts light on the optical path of light.

  Further, on the surface facing the intermediate transfer belt 41 which is the lower surface of the case 84 in the figure, a dirt prevention film 85 is provided so as to cover the opening of the exit slit 84a and the entrance slit 84c. By providing the antifouling film 85, it is possible to prevent the toner and the like from entering the inside of the exit slit 84a and the entrance slit 84c and contaminating the LED 81 and the PD 83.

<Description of functions such as a main control unit that executes misregistration control>
Next, functions of the main control unit 60 and the detection sensor unit 80 that execute the positional deviation control will be described.
FIG. 4 is a block diagram illustrating functions of the main control unit 60 and the detection sensor unit 80. In FIG. 4, only a block related to the above-described misregistration control among a plurality of controls executed by the main control unit 60 is shown.
The main control unit 60 is a CPU (Central Processing Unit) 61 that performs arithmetic processing when performing image forming operation control, positional deviation control, and the like by the image forming apparatus 1, and positional deviation control executed by the CPU 61. A ROM (Read Only Memory) 63 storing a software program and a RAM (Random Access Memory) 62 storing various counter values and temporary data generated during the execution of the program are provided.

The main control unit 60 also includes an image output circuit 64 that outputs image information in an actual image forming operation and image information for forming an image quality adjustment pattern T based on a command from the CPU 61, and an image quality adjustment pattern. An image quality adjustment pattern data storage unit 65 that stores image information (image data for control marks) for forming T in advance is provided. The image output circuit 64 outputs image information for actual image forming operation and image information for forming the image quality adjustment pattern T to the laser exposure device 26 corresponding to each image forming unit 30. The image output circuit 64 and the image quality adjustment pattern data storage unit 65 here function as index forming means.
Further, the main control unit 60 includes a light source driving circuit 66 that controls lighting of the LED 81 provided in the detection sensor unit 80.

  On the other hand, the detection sensor unit 80 includes a detection circuit 89 in addition to the reading function units shown in FIGS. 3 and 4 for reading the image quality adjustment pattern T. The detection circuit 89 converts a current value corresponding to the amount of received light output from the PD 83 (see FIG. 3) into a voltage value corresponding to the magnitude, and further amplifies it to generate a pattern detection signal. Then, by detecting the minimum value and maximum value of the generated pattern detection signal, a peak detection signal and a hold signal holding the minimum value and maximum value of the pattern detection signal are further generated, and these are output to the main control unit 60. To do.

  FIG. 5 is a diagram for explaining the configuration of the detection circuit 89 provided in the detection sensor unit 80. As shown in FIG. 5, the detection circuit 89 converts / amplifies the current value corresponding to the amount of received light output from the PD 83 to a voltage value corresponding to the magnitude, and outputs the voltage value as a pattern detection signal. 181, a peak detection circuit unit 182 that detects a minimum value or a maximum value of a pattern detection signal output from the amplification circuit unit 181 and outputs a peak detection signal, and a pattern detection signal output from the amplification circuit unit 181 In addition, a sample hold circuit unit 183 that outputs a hold signal holding the minimum value or maximum value of the pattern detection signal when the peak detection signal is output from the peak detection circuit unit 182 is provided. The detection circuit 89 outputs these peak detection signal and hold signal to the main control unit 60 (CPU 61).

<Description of processing procedure for executing misregistration control>
FIG. 6 is a flowchart illustrating a processing procedure when the main control unit 60 executes misalignment control for images formed by the image forming units 30Y, 30M, 30C, and 30K.
As shown in FIG. 6, the main control unit 60 (image output circuit 64) forms an image quality adjustment pattern T composed of position control marks M of each color formed with a black (K) toner image for each image formation. It is formed at a predetermined location on the intermediate transfer belt 41 by the unit 30 (step 101). At this time, the correction value of the positional deviation amount in each image forming unit 30 is reset.

  The image quality adjustment pattern T formed on the intermediate transfer belt 41 is read by the detection sensor unit 80 (see FIG. 2) (step 102).

Next, the main control unit 60 (CPU 61) determines the absolute values for the target values in the main scanning direction and the sub-scanning direction of the black (K) position control mark MK as the reference color based on the reading result by the detection sensor unit 80. And a relative displacement amount in the main scanning direction and the sub-scanning direction of each of the Y, M, and C position control marks M with respect to the K position control mark MK as the reference color is calculated. (Step 103). Then, based on the amount of positional deviation in the main scanning direction and the amount of positional deviation in the sub-scanning direction obtained for each color, a toner image (electrostatic latent image) on the photosensitive drum 31 in each image forming unit 30 is formed. The position, that is, the exposure timing of each photosensitive drum 31 by each laser exposure device 26 is reset in both the main scanning direction and the sub-scanning direction (step 104). Thereby, the formation position of each color toner image in each image forming unit 30 is corrected. Accordingly, color misregistration of each color toner image on the intermediate transfer belt 41 is suppressed. That is, the CPU 61 functions as a misregistration correction unit that corrects misregistration of an image formed by the image forming unit 30.
As described above, the positional deviation correction (registration control) in each image forming unit 30 is performed in steps 101 to 104 described above.

<Description of image quality adjustment pattern>
Next, FIG. 7A is read from the image quality adjustment pattern data storage unit 65 by the image output circuit 64 of the main control unit 60 and is applied onto the intermediate transfer belt 41 by the image forming units 30Y, 30M, 30C, and 30K. It is a figure which shows an example of the pattern T for image quality adjustment of the formed this Embodiment. FIG. 7B is a diagram showing an example of a conventional image quality adjustment pattern T.
As shown in FIGS. 7A and 7B, the image quality adjustment pattern T read by the detection sensor unit 80 (see FIG. 4) is yellow (Y), magenta (M), cyan (C), black. In the direction of movement of the intermediate transfer belt 41 (sub-scanning direction) by position control marks MY, MM, MC, MK (hereinafter also collectively referred to as “position control marks M”) composed of toner images of the respective colors (K). Formed along. The position control mark M functions as an image correction index used for correcting the positional deviation of the image formed by the image forming unit 30.

  The position control marks M are formed, for example, so as to be alternately arranged so as to sandwich the black (K) position control mark MK as a reference. Further, the position control mark M is formed obliquely with respect to both the moving direction of the intermediate transfer belt 41 (sub-scanning direction: process direction) and the direction orthogonal to the moving direction (main scanning direction: lateral direction). It is composed of a first side Ma and a second side Mb that form a letter “C”. The first side Ma and the second side Mb each have an inclination angle of 27 ° with respect to the main scanning direction, and the first side Ma and the second side Mb have an angle of 54 °. Make an angle. With this configuration, the position control mark M functions as an image correction index (mark) for detecting the amount of positional deviation in both the main scanning direction (lateral direction) and the sub-scanning direction (process direction).

  However, the position control mark M of the present embodiment shown in FIG. 7A is different from the conventional position control mark M shown in FIG. 7B in the position control marks MY, MM, and MC. The numbers of the one side Ma and the second side Mb are different. That is, in the conventional image quality adjustment pattern T shown in FIG. 7B, the first side Ma and the second side Mb of the position control marks MY, MM, MC are formed one by one. On the other hand, the number of the position control marks M of this embodiment shown in FIG. 7A is two for the same color. Here, these are illustrated as position control marks Ma1, Ma2, Mb2, and Mb1. That is, the position control mark M according to the present embodiment has each of the first side Ma and the second side Mb as one pattern (type), and the Y color that is a color other than the K color for the one pattern, Two are formed in succession for M and C colors. On the other hand, one K color is formed for each pattern.

<Description of Operation of Detection Sensor Unit for Reading Position Control Mark>
Next, the operation of the detection sensor unit 80 that reads the position control mark M of the image quality adjustment pattern T will be described.
FIG. 8 is a timing chart for explaining a signal generated when the detection sensor unit 80 reads the position control mark M. FIG. 8A shows a pattern detection signal generated when the detection sensor unit 80 reads the position control mark M of the image quality adjustment pattern T. FIG. 8B shows a minimum value of the pattern detection signal. A peak detection signal output by detecting a maximum value (peak) is shown.

Here, for example, when viewing the peak detection signal for the position control mark MY relating to the Y color, as shown in FIG. 8A, in the detection sensor unit 80, the position control mark M of the image quality adjustment pattern T is PD83. When entering the visual field region R1, first, the overlapping area between the visual field region R1 and the first side Ma1 of the position control mark M is expanded, so that the pattern detection signal relating to the position control mark M gradually falls. Then, at the position where the visual field region R1 is substantially covered by the first side Ma1 of the position control mark M, the pattern detection signal by the position control mark M is minimum. In this case, the thickness of the first side Ma1 constituting each position control mark M is set slightly smaller than the diameter of the visual field region R1 of the PD 83. For this reason, after passing the position where the pattern detection signal of the first side Ma1 of the position control mark M is minimized, the overlapping area between the visual field region R1 and the position control mark M decreases thereafter, and pattern detection is performed. The signal rises gradually. Then, at the position where the first side Ma1 of the position control mark M is completely removed from the visual field region R1 of the PD 83, the pattern detection signal becomes maximum and takes a maximum value.
Then, when the position control mark M further moves and the first side Ma2 of the position control mark M enters the visual field region R1 of the PD 83, the pattern detection signal starts to change again. When the position control mark M further moves, the overlapping area between the visual field region R1 and the first side Ma2 of the position control mark M increases, so that the pattern detection signal gradually decreases. The pattern detection signal is minimized at a position where the visual field region R1 is substantially covered by the first side Ma2. Thereafter, the overlapping area between the visual field region R1 and the first side Ma2 of the position control mark M decreases, and the pattern detection signal gradually increases and becomes maximum again.

  Then, as shown in FIG. 8B, the position where the center position in the thickness direction of the first side Ma1 of the position control mark M coincides with the center position of the visual field region R1 of the PD 83, and the first side An instantaneous minimum value in the pattern detection signal is generated at the position where the center position of Ma2 in the thickness direction matches the center position of the visual field region R1 of the PD 83. Further, there is a place where the pattern detection signal has a maximum value at a position between these. The peak detection circuit unit 182 (see FIG. 5) of the detection circuit 89 provided in the detection sensor unit 80 detects an instantaneous maximum value (peak) in the pattern detection signal related to the position control mark M, and this maximum value is detected. A peak detection signal that rises from a low level (“L”) to a high level (“H”) is generated in synchronization with the moment when the value occurs. As a result, the rising edge portion of the peak detection signal indicates the position between the first side Ma1 and the first side Ma2 of the position control mark M, and the detection sensor unit 80 has the first sensor Ma. A position between the side Ma1 and the first side Ma2 is detected. Then, the detection sensor unit 80 outputs the generated peak detection signal to the main control unit 60. Actually, by detecting the maximum value of the pattern detection signal, the center positions of the first side Ma1 and the first side Ma2 and the second side Mb1 and the second side Mb2 are detected. Here, the reason why the detection signal falls when reading the position control mark M is that the intermediate transfer belt 41 is glossy and reflects light well. That is, since the reflectance of the position control mark M is smaller than that of the intermediate transfer belt 41, the detection signal is lowered when the position control mark M is read. In the example described above, the first sides Ma1 and Ma2 of the position control mark M have been described, but the same applies to the second sides Mb1 and Mb2.

  As shown in the figure, the peak detection signal for the position control mark MK relating to the K color has a minimum value of the pattern detection signal for each of the first side Ma and the second side Mb of the position control mark M. It will be. Therefore, for the position control mark MK, the minimum value in the pattern detection signal is detected, and the center positions of the first side Ma and the second side Mb are detected.

<Description of pattern detection signal>
Next, the pattern detection signal generated when the detection sensor unit 80 reads the position control mark M of the image quality adjustment pattern T will be described in more detail.
FIG. 9A is a diagram for explaining the pattern detection signal of the present embodiment, and is an enlarged view of the pattern detection signal shown in FIG. That is, the illustrated pattern detection signal is a pattern detection signal when the position control mark M in FIG. Here, a pattern detection signal D1Y when the position control mark MY related to Y color is read, and a pattern detection signal D1K when the position control mark MK related to K color is read are shown.

  Further, the pattern detection signal shown in FIG. 10A is a pattern detection signal when the conventional image quality adjustment pattern T shown in FIG. 7B is used. Here, a pattern detection signal D2Y when the position control mark MY related to the Y color is read and a pattern detection signal D2K when the position control mark MK related to the K color is read are shown.

  Comparing the pattern detection signal D2Y and the pattern detection signal D2K shown in FIG. 10A, the pattern detection signal D2Y has a larger minimum detection peak at the center than the pattern detection signal D2K. In addition, the pattern detection signal D2Y has a higher detection value than the pattern detection signal D2K even at a location where the position control mark M is not present. The pattern detection signal D2Y is not symmetrical with respect to the peak position, and the detected value is higher on the right side in the figure than the peak position.

  This is because the detection sensor unit 80 captures the diffuse reflection component shown in FIG. 10C in addition to the regular reflection component shown in FIG. This diffuse reflection component is, for example, light diffusely reflected by irradiating the adjacent position control mark M with light. Since the diffuse reflection component is not symmetrical with respect to the peak position, the pattern detection signal D2Y of FIG. 10A in which the regular reflection component and the diffuse reflection component are combined is also not symmetrical. This is the same for the M color and the C color as well as the Y color. On the other hand, the reason why such a phenomenon does not occur in the pattern detection signal D2K is that the position control mark M for the K color hardly generates diffuse reflection light for the K color.

  In this way, when the conventional position control mark M is read, the waveform of the pattern detection signal differs for the K color and other colors other than the K color. And for colors other than the K color, diffuse reflection components whose waveforms are not symmetrical are entered, so that the peak position deviates from the original position. Therefore, the peak detection positions for the K color and other colors are different. For this reason, it is not possible to correct the positional deviation normally.

  On the other hand, when the pattern detection signal D1Y and the pattern detection signal D1K shown in FIG. 9A are compared, the pattern detection signal D1Y is symmetrical with respect to the position of the maximum value.

  The pattern detection signal D1Y is a combination of the regular reflection component shown in FIG. 9B and the diffuse reflection component shown in FIG. 9C. Here, unlike FIG. 10C, the diffuse reflection component shown in FIG. 9C is symmetrical with respect to the position of the maximum value. This is because the waveform of the diffuse reflection component becomes broad when two pattern detection signals D1Y continue at close intervals. Therefore, the waveform of the diffuse reflection component is almost flat near the maximum value of the pattern detection signal D1Y. It becomes. Therefore, the pattern detection signal D1Y shown in FIG. 9A is symmetrical with respect to the position of the maximum value. That is, even if there is a diffuse reflection component, the position of the maximum value hardly changes.

  For the above reasons, when the position control mark M according to the present embodiment is read, the waveforms of the pattern detection signals are both symmetrical for all colors. In the present embodiment, for the K color, the position deviation is corrected using the position where the pattern detection signal D1K is the minimum value as the detection position. On the other hand, for Y color, M color, and C color, the position deviation is corrected using the position of the maximum value of the pattern detection signal as the detection position. As a result, the detection positions of the K color and other colors other than the K color are unlikely to shift, and therefore, the misregistration can be corrected normally. As described with reference to FIG. 7A, the position control mark M according to the present embodiment is continuous for Y, M, and C colors other than K for one pattern. Two are formed. On the other hand, one K color is formed for each pattern. This is because diffuse reflected light is likely to be generated for the Y, M, and C colors, but diffuse reflected light is less likely to be generated for the K color and may be the same as the conventional position control mark M. Because.

<Explanation of Detection and Correction of Misalignment>
Next, the detection and correction of the positional deviation amount by the peak detection signal from the detection sensor unit 80 will be described.
FIG. 11 is a diagram for explaining a method of calculating a positional deviation amount using the position control mark M. FIG.
The following description is a method for calculating the amount of misregistration for the Y, M, and C colors. That is, first, the position of the maximum value of the pattern detection signal is obtained, and the amount of displacement is calculated based on the position of the maximum value. In practice, the CPU 61 obtains the position where the maximum value is obtained from the peak detection signal shown in FIG. 9B, and performs the following calculation. Therefore, in this case, the CPU 61 functions as a position specifying unit that specifies the position between two consecutive position control marks M from the pattern detection signal.

  In FIG. 11, the position indicated by the solid line is the position of the maximum value of the pattern detection signal, and the position indicated by the broken line is the ideal position (ideal position).

As shown in FIG. 11, the distance from the reference position preset on the intermediate transfer belt 41 to the detection position A between the two first sides Ma is DA, and the two second positions from the reference position. Assuming that the distance to the detection position B between the sides Mb is DB, the shift amount (hereinafter referred to as “main scan shift amount”) Lerr of the position control mark M in the main scanning direction (lateral direction) is the first side Since Ma and the second side Mb are formed symmetrically, this corresponds to the difference between DA and DB. That is, in the ideal position, it is assumed that between the two first sides Ma is detected at the detection position A ′ and between the two second sides Mb is detected at the detection position B ′. When the difference from DB is DW, the main scanning deviation amount Lerr is obtained by the following equation (1).
Lerr = ((DB-DA-DW) × 0.5) × tan θ (1)
Here, θ is an angle formed by the first side Ma and the second side Mb with respect to the sub-scanning direction, and 90 ° −27 ° = 63 ° in the present embodiment. Further, DW assumes that the visual field region R1 of the PD 83 of the detection sensor unit 80 is installed at an intermediate position in the main scanning direction of the ideal state position, and sets cos θ to the length of the first side Ma or the second side Mb. Calculated by multiplying.

Further, the deviation amount (hereinafter referred to as “sub-scanning deviation amount”) Perr of the position control mark M in the sub-scanning direction (process direction) is also obtained based on DA and DB. That is, if the intermediate position between the detection position A ′ and the detection position B ′ when the ideal position is detected is C ′ and the distance from the reference position to the intermediate position C ′ is DP, the sub-scanning deviation amount Perr Is obtained by the following equation (2) since the first side Ma and the second side Mb are formed symmetrically.
Perr = 0.5 × (DA + DB) −DP (2)
Note that the distance from the reference position in the ideal state to the detection position A ′ between the two first sides Ma is DA ′, and the detection position B ′ between the reference position and the two second sides Mb. If the distance up to DB ′ is DP ′, DP = (DA ′ + DB ′) / 2.

  Actually, the detection sensor unit 80 outputs to the main control unit 60 the peak detection signal at the detection position A between the two first sides Ma and the detection position B between the two second sides Mb. To do. Accordingly, the main control unit 60 uses the timing at which the peak detection signals at the detection position A and the detection position B are received from the detection sensor unit 80, and the main scanning deviation amount Lerr (1) and the sub-scanning deviation amount Perr (1). Is calculated. That is, the main control unit 60 measures the reception timing of the peak detection signal at the detection position A and the detection position B as times TA and TB from the reference position, respectively. Here, when the moving speed (process speed) of the intermediate transfer belt 41 is V, DA = TA × V and DB = TB × V. The time TW required for the intermediate transfer belt 41 to move the distance DW is obtained by dividing the length of the first side Ma or the second side Mb by cos θ by the process speed V. .

Therefore, the main control unit 60 uses the reception timings TA and TB of the peak detection signals at the detection position A and the detection position B with the reference position as a reference, to set the main scanning deviation amount Lerr (1) as the following (3). The sub-scanning deviation amount Perr (1) is obtained by the equation (4).
Lerr (1) = ((TB−TA−TW) × V × 0.5) × tan θ (3)
Perr (1) = (0.5 × (TA + TB) −TP) × V (4)
The time TP here is the time required for the intermediate transfer belt 41 to move the distance DP from the reference position to the intermediate position C ′, and is TP = (DA ′ + DB ′) / 2V.

  Further, the main control unit 60 performs the main scanning deviation amount Lerr (1) and the sub-scanning deviation amount Perr (1) with reference to the ideal position control mark M ′ obtained by the equations (3) and (4). ) Based on the reference black (K) position control mark MK and the position control marks MY, MM, MC relative to the main scanning shift amount Lerr (1) ′ and the sub-scanning shift amount Perr ( 1) 'is calculated.

  In the above-described example, the calculation method of the positional deviation amount in the case of Y color, M color, and C color has been described. However, in the case of K color, the above calculation is performed for the position where the pattern detection signal is the minimum value. Similarly, the amount of displacement can be calculated.

<Description of Examples of Other Image Quality Adjustment Patterns>
The image quality adjustment pattern T is not limited to that shown in FIG. For example, it is conceivable to change depending on the wavelength of the LED 81.
FIG. 12 is a diagram showing the spectral reflectance with respect to the wavelength of light for toners of Y, M, C, and K colors. In FIG. 12, the horizontal axis represents the wavelength of light, and the vertical axis represents the spectral reflectance.

  Here, when the LED 81 having the emission center wavelength of 940 nm as described with reference to FIG. 3 is irradiated with light to the position control mark M formed by the toner of each color, the Y color, M color, and C color are respectively Spectral reflectance is about 75%. On the other hand, the spectral reflectance of the K color is almost 0%. In this case, when the LED 81 irradiates the position control mark M with light, almost no diffuse reflected light is generated for the K color because the spectral reflectance is low. On the other hand, for the Y, M, and C colors, a large amount of diffuse reflected light is generated due to the high spectral reflectance. Therefore, as shown in FIG. 7, it is effective to form two position control marks M of the image quality adjustment pattern T in succession for one pattern for the Y, M, and C colors. Further, there is no need for the K color, and one color is sufficient for one pattern.

  Here, consider a case where, for example, an LED 81 having an emission center wavelength of 680 nm is used as the LED 81. In this case, when the position control mark M formed by the toner of each color is irradiated with light, the spectral reflectance is about 75% for the M color and the Y color. On the other hand, the spectral reflectance of C color and K color is almost 0%. Accordingly, it is effective to form two position control marks M for the image quality adjustment pattern T in succession for one pattern for the Y and M colors, but it is necessary for the C and K colors. Instead, only one pattern is required.

FIG. 13 is a diagram illustrating an example of an image quality adjustment pattern T when an LED 81 having an emission center wavelength of 680 nm is used.
As shown in the figure, the image quality adjustment pattern T has two first and second sides Ma and Mb of position control marks MY and MM, which are Y and M color position control marks. Yes. Here, these are illustrated as position control marks Ma1, Ma2, Mb2, and Mb1. On the other hand, the first side Ma and the second side Mb of the position control marks MC and MK, which are C and K color position control marks, are formed one by one.

  In the example described in detail above, two position control marks M are formed for one pattern, but this does not prevent the formation of three or more positions. In this case, for example, the CPU 61 specifies a position between the first two consecutive image correction indexes from the pattern detection signal, and the main control unit 60 performs the positional deviation correction based on the detected position. Good.

  Further, the processing performed by the main control unit 60 in the present embodiment is realized, for example, by cooperation between software and hardware resources. In other words, the CPU 61 (not shown) in the control computer provided in the main control unit 60 loads the program for realizing each function of the main control unit 60 into the RAM 62 and executes it.

  Therefore, the processing performed by the main control unit 60 is a position control mark used for correcting misalignment of an image formed by the image forming unit 30 that forms an image using a plurality of predetermined colors. The function of forming two or more M continuously in the same color for one pattern by the image forming unit 30, the LED 81 that emits light toward the position control mark M, the intermediate transfer belt 41, and the position control mark A function of acquiring a detection signal from the detection sensor unit 80 including a PD 83 that receives the reflected light reflected from the M and detects the position control mark M, and a PD 83 of the detection sensor unit 80. A function for specifying a position between two consecutive position control marks M from the obtained detection signal, and a position between the two specified position control marks M Et al., A function of performing positional deviation correction for the image to be formed in the image forming unit 30, can be considered as a program for actualizing.

  The program for realizing the present embodiment can be provided not only by communication means but also by storing it in a recording medium such as a CD-ROM.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 26 ... Laser exposure apparatus, 30 (30Y, 30M, 30C, 30K) ... Image forming unit, 41 ... Intermediate transfer belt, 60 ... Main control part, 61 ... CPU, 64 ... Image output circuit, 65 ... image quality adjustment pattern data storage unit, 80 ... detection sensor unit, 81 ... LED, 83 ... PD, T ... image quality adjustment pattern, M ... position control mark

Claims (5)

An image forming unit that forms an image using a plurality of predetermined colors;
Index forming means for forming two or more image correction indexes, which are used for correcting the positional deviation of an image formed by the image forming unit, continuously in the same color for one mold by the image forming unit;
An image carrier to which the image correction index formed by the image forming unit is sequentially transferred;
A light source that emits light toward the image correction index, and a light receiving unit that receives reflected light reflected from the image holding body and the image correction index and serves as a detection signal for detecting the image correction index And a detection means comprising:
Position specifying means for specifying a position between two consecutive image correction indices from a detection signal obtained from the light receiving unit of the detection means;
A misregistration correction unit that performs misregistration correction of an image formed by the image forming unit from a position between the two image correction indices specified by the position specifying unit;
An image forming apparatus comprising:   2. The image forming apparatus according to claim 1, wherein the index forming unit forms a color other than black as the two consecutive image correction indexes.   The image forming apparatus according to claim 1, wherein the detection unit does not include an optical element that refracts the light on an optical path of the light.   4. The position specifying unit specifies a position between two consecutive image correction indices by detecting a maximum value of the detection signal. Image forming apparatus. On the computer,
Two consecutive image correction indices of the same color for one mold are used for correcting the displacement of an image formed in an image forming unit that forms an image using a plurality of predetermined colors. The function to be formed by the image forming unit,
A light source that emits light toward the image correction index, a light receiving unit that receives reflected light reflected from the image carrier and the image correction index, and serves as a detection signal for detecting the image correction index; A function of obtaining the detection signal from a detection means comprising:
A function for specifying a position between two consecutive image correction indices from a detection signal obtained from the light receiving unit of the detection means;
A function of correcting a positional deviation of an image formed by the image forming unit from a position between the specified two image correction indexes;
A program that realizes

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